Field of the Invention
The present invention relates to a sheet feeder having a configuration for preventing a sheet feeding failure.
Description of the Related Art
An image forming device, such as a printer or a copier, is provided internally or externally with a sheet feeder for continuously conveying sheets stacked on a stack tray one by one. The sheet feeder has an elevating stack tray on which the sheets are stacked, a delivery roller that is brought into contact with an upper surface of the sheet stack to deliver the sheets, a feeding roller and a separating member that separate and feed one by one the delivered sheets, and a conveying roller pair that conveys the fed sheet toward the image forming apparatus. The sheets on the stack tray are sequentially guided toward the image processing section by the above delivery, separating, and conveying rollers.
As a separating mechanism that separates the sheets one from another, there is known so-called a friction separation system constituted by a feeding roller that feeds the sheet as described above and a separating member which is a separating pad or a separating roller that is brought into contact with an outer peripheral surface of the feeding roller. In such a friction separation system, a surface of the feeding roller or separating member is worn due to age or contact to the sheet, thus deteriorating separating performance. With the deterioration in the separating performance, double-feeding where two or more sheets are fed at the same time in an overlapped manner frequently occurs.
Further, in recent years, types of the sheets to be handled in the image forming apparatus are diversified, and there is a demand for a sheet feeder capable of separating and feeding special sheets, such as OHP sheets, tracing papers, or coated papers. However, such special sheets are more likely to be double-fed than regular papers.